1. Technical Field
This invention relates generally to millimeter wave electronic devices and, more particularly, to a hermetically sealable millimeter waveguide transition for channelling high frequency signals through a waveguide wall.
2. Discussion
The demand for Gallium Arsenide (GaAs) Monolithic Microwave Integrated Circuit (MMIC) devices is expected to drastically increase during the next few decades. This technology is capable of ever increasing operating frequencies and is frequently utilized in radars, electronic warfare, missiles and array weapons as well as a wide variety of non-military applications. As the monolithic circuitry in these devices becomes increasingly dense, and as operating frequencies increase to W-band (94 GHz) and beyond of the millimeter wave range, signal capture loss becomes a progressively more severe problem. This places a heavy burden on existing millimeter wave packaging technology, and especially on radio frequency (RF) input/output transitions, often the source of this loss.
Transitions for channelling high frequency signals from one waveguide to another formed by mechanically joining the waveguides together are typically bulky and incapable of operating at very high frequencies. Teflon.RTM. (tetrafluoroethylene or (TFE) pin feedthroughs sometimes used as a transition to interconnect two waveguides solve the space problem but have a number of inherent weaknesses. Many are found to have electrical mismatching, discontinuity problems, high RF losses and the ability only to operate below 30 GHz in frequency. This type of conventional RF transition arrangement also has a limited scope of usage because it is generally non-hermetic and unable to withstand elevated temperatures of 125.degree. C. and beyond, often required in high RF device packaging and a must for space flight applications.
Millimeter wave housing packages, in which a GaAs MMIC chip or other high frequency electronic device is to be sealed for communication with a waveguide, without built-in hermeticity may require waveguide sealing windows used to hermetically seal off open ends of the waveguides. This, however, requires incoming and/or outgoing RF signals to pass through the sealed waveguide window, thereby creating signal distortion and loss. Additionally, extensive waveguide window development and reliability testing of the resulting package is often necessary, thereby leading to higher overall costs for these types of millimeter wave housings.
Current waveguide-to-device transition designs for millimeter wave housing packages which have addressed hermeticity generally have not been applicable to colinear applications in which the incoming and outgoing waveguide channels are disposed along a common linear axis orthogonal to the RF transition feedthrough. With non-colinear transition designs, 90 degree adapters are necessary and must be fabricated, thereby creating taller fixture housings and increasing material and machining costs. Increased volume and weight of the resulting housings makes their use undesirable for typical colinear system applications wherein size and weight are restricted.
There is therefore a need for a compact and hermetically sealable millimeter wave transition capable of operating in elevated temperatures and having low loss in the 30 GHz to 150 GHz frequency range. It would also be advantageous for this transition to be useful in providing an inexpensive low-profile colinear millimeter wave package with built-in hermeticity, useful in a variety of military and commercial applications from smart weapons to spaceborn RF payloads.